2.2 Experimental plants and substrates
V. natans is a common submerged macrophyte species, which is widely distributed in the middle reaches of the Yangtze River. It is widely used for the restoration of lake ecosystems due to its rapid growth and developed root system, and it can absorb excess nutrients from the water body (Yan et al. 2013). The V. natans was incubated in a constant temperature room (25 °C) at a light intensity of 3500 lx with the light-dark duration ratio of 1:1 for a week. After incubation, the healthy and equal-sized submerged plants were selected, pruned to a uniform plant height of 10 cm, and transplanted into the polyethylene column (15 cm in diameter, and 50 cm in height).
The experiments were carried out in polyethylene column with 5 V. natans plants (10 cm in height) plants in each column containing a sediment layer of 20 cm thickness. The 4 treatment groups consisted of maifanite (ME), vermiculite (VE), ceramsite (CE), and volcanic rock gravels (VR) substrates (3-5mm in particle size). The group without additional substrate was control group (CK). These substrates all were produced in Henan province, China. The sediment surface was covered with 15 g substrate to make it 1 cm thick, and then distilled water was added to make the column water depth reach 24 cm. The experiment was performed in triplicates. V. natans planting experiment started on June 25, 2022 and lasted for 40 days with plant sampling every 10 days.